Industries, including for example the steel, power and chemical industries utilize process equipment that may require one or more water cooled elements to be placed in varying and potentially extreme heat flux conditions with aggressive atmospheres that may for example have high concentrations of acids, particulates and other chemicals that may diminish the operating life of the device. For example, the steel, foundry and metal refining industry has challenges with water cooled and non-water-cooled equipment operating in high mechanical wear, high corrosive, high temperature, high electrically conductive and/or thermally stressing environments within the melting furnace. These extreme and varying conditions make it desirable to have the option to design devices with various materials and operating characteristics with the potential, for example, to optimize the cost/benefit requirements for economic operations.
In the case of steel, for example, steel illustratively is made by melting and refining iron and steel scrap in a metallurgical furnace. Illustratively, the furnace may be an electric arc furnace (EAF) or a basic oxygen furnace (BOF). It is desirable to keep such furnaces operational for as long as possible. One way to extend the operational life of a furnace is to guard against thermal, chemical and mechanical stresses through the use, for example, of heat exchange devices of various and varying designs.
Structural damage caused during the charging process affects the operation of an EAF. Since scrap has a lower effective density than molten steel, the EAF must have sufficient volume to accommodate the scrap and still produce the desired amount of steel. As the scrap melts it forms a hot metal bath in the hearth or smelting area in the lower portion of the furnace. As the volume of steel in the furnace is reduced, however, the free volume in the EAF increases. The vessel wall, cover or roof, duct work, and off-gas chamber are at risk from thermal, chemical, and mechanical stresses caused by charging and melting the scrap and refining the resulting steel. Such stresses may limit the operational life of the furnace. It is desired to protect the portion of the furnace above the hearth or smelting area against the high internal temperatures of the furnace.
Historically, the EAF was generally designed and fabricated as a welded steel structure which was protected against the high temperatures of the furnace by a refractory lining. In the late 1970's and early 1980's, the steel industry began to combat operational stresses by replacing expensive refractory brick with water cooled roof panels, and water cooled sidewall panels located in portions of the furnace vessel above the smelting area. Water cooled components have also been used to line furnace duct work in the off-gas systems. Existing water cooled components are made with various grades and types of plates and pipes. An example of a cooling system is disclosed in U.S. Pat. No. 4,207,060, now incorporated herein by reference, which uses a series of cooling coils. Generally, the coils are formed from adjacent pipe sections with a curved end cap, which forms a path for a liquid coolant flowing through the coils. This coolant is forced through the pipes under pressure to maximize heat transfer. Such pipes and plates have been formed using carbon steel and stainless steel, or more expensive metals such as copper. In this disclosure, the terms tube, tubing, pipes, and piping are synonymous, and may be used interchangeably. In addition, the heat exchangers, as recognized by those skilled in the art, to stabilize operating temperatures.
In some process applications, it is advantageous for a foreign substance such as for example slag, which is a by-product of the melting process, to collect on the operating side (“hot side”) or operating portion of the equipment to harness the non-conductive and insulating properties of slag in order to protect the equipment from damage, wear and premature failure during operation. The collected or retained slag also protects against the accidental and potential catastrophic effects of inadvertent splashing of liquid metal against the operating or hot side of the equipment caused by excessive boiling or slopping of the molten metal during the process. A suitable example of cooling pipes designed to encourage slag retention is found in commonly owned U.S. Pat. No. 6,330,269, the disclosure of which is now expressly incorporated herein by reference.
The steel, foundry and metal refining industry also has challenges with water cooled and non-water-cooled equipment collecting unwanted slag and/or other foreign materials on the hot face of the equipment during operation. This slag, siliceous, metallic and/or other foreign materials that enter the process can be detrimental to the operation should it become detached and fall into the liquid steel that is contained within the furnace or duct structure. For example, the accidental intrusion of such material into the molten metal could contaminate or otherwise cause the molten metal in the vessel to become off-specification resulting in its being scrapped or requiring additional high cost processing to refine the molten metal back to its acceptable composition. The dropping of this material into the furnace could also cause excessive boiling or slopping of the molten metal creating a safety hazard in and around the vessel. In addition, the detaching of the foreign materials can be a safety issue should it fall when the equipment is off-line and either damage equipment or hurt workers in the area. Thus, it may be desirable to have heat exchange systems that either encourage or discourage the retention of slag on operating surfaces as desired. One suitable example of such a system is found in commonly owned International Patent Application PCT/US06/060461 of Manasek filed Nov. 1, 2006, the disclosure of which is now expressly incorporated herein by reference. Among other embodiments, PCT/US06/060461 discloses one illustrative embodiment comprising an extruded, drawn or cold rolled tube or pipe that has notches or indentions in its conduction surface to promote the adhesion of slag, siliceous or other foreign materials during normal operations in a metal processing device. A plurality of the illustrative tubes or pipes illustratively may be coupled, butted and/or welded together to form a notched surface that promotes adhesion of slag, siliceous or other foreign material. Another illustrative embodiment comprises an extruded, drawn or cold rolled tube or pipe that has a substantially flat surface configured to deter or resist the adhesion of slag, siliceous or other foreign material during normal operations of a metal processing device, system or equipment. A plurality of the illustrative pipes may be coupled, butted and/or welded together to form a generally smooth planar surface configured to deter or resist the adhesion of slag, siliceous or other foreign material. Illustratively, any combination and configuration of the notched and the generally smooth-surface pipes may be used as appropriate in the various areas of the metal processing device, system or equipment. Methods of use are also claimed.
Today's modern EAF furnaces also incorporate pollution controls to capture the off-gasses that are created during the process of making steel. For example, fumes from the furnace are generally captured in two illustrative ways. Both of these processes are employed during the operation of the furnace. One illustrative form of capturing the off-gasses is through a furnace canopy. The canopy is similar to an oven hood. It is part of the building and catches gasses during charging and tapping. The canopy also catches fugitive emissions that may occur during the melting process. Typically, the canopy is connected to a bag house through a non-water cooled duct. The bag house is comprised of filter bags and several fans that push or pull air and off-gasses through the filter bags to cleanse the air and gas of any pollutants.
The second illustrative form of capturing the off-gas emissions is through the primary furnace line. During the melting cycle of the furnace, a damper illustratively closes the duct to the canopy and opens a duct in the primary line. This is a direct connection to the furnace and is the main method of capturing the emissions of the furnace. The primary line is also used to control the pressure of the furnace. This line is made up of water cooled duct work to guard against temperatures that can reach as high as about 4,000° F. and then drop to ambient in a few seconds. The gas streams generally include various chemical elements, including hydrochloric and sulfuric acids. There are also many solids and sand type particles. The velocity of the gas stream can be upwards of 150 ft./sec. These gasses will be directed to the main bag house for cleansing, as hereinabove described.
The above-described environments place a high level of strain on the water cooled components of the primary ducts of the EAF. The variable temperature ranges in the metallurgy industry can cause expansion and contraction issues in the components which lead to material failure. Moreover, the dust particles continuously erode the surface of the pipe in a manner similar to sand blasting. Acids flowing through the system also increase the attack on the material, additionally decreasing the overall lifespan.
Concerning BOF systems, improvements in BOF refractories and steelmaking methods have extended operational life. However, the operational life is limited by, and related to, the durability of the off-gas system components, particularly the duct work of the off-gas system. With respect to this system, when failure occurs, the system illustratively must be shut down for repair to prevent the release of gas and fumes into the atmosphere. Current failure rates cause an average furnace shut down of 14 days. As with EAF type furnaces, water cooled components have historically been comprised of water cooled carbon steel, or stainless steel type panels.
Using water cooled components in either EAF or BOF type furnaces has reduced refractory costs, and has also enabled steelmakers to operate each furnace for a greater number of heats than was possible without such components. Furthermore, water cooled equipment illustratively has enabled the furnaces to operate at increased levels of power. Consequently, production has increased and furnace availability has become increasingly important. Notwithstanding the benefits of water cooled components, these components have consistent problems illustratively with wear, corrosion, erosion, and other damage. Another problem associated with furnaces is that as available scrap to the furnace has been reduced in quality, more acidic gasses are created. This is generally the result of a higher concentration of plastics in the scrap. These acidic gasses must be evacuated from the furnace to a gas cleaning system so that they may be released into the atmosphere. These gasses illustratively are directed to the off-gas chamber, or gas cleaning system, by a plurality of fume ducts containing water cooled pipes. However, over time, the water cooled components and the fume ducts may give way to acid attack, metal fatigue, or erosion for example. Certain materials, for example, carbon steel and stainless steel, have been utilized in an attempt to resolve the issue of the acid attack. More water and higher water temperatures have been used with carbon steel in an attempt to reduce water concentration in the scrap, and to reduce the risk of acidic dust sticking to the side walls of a furnace. The use of such carbon steel in this manner has proven to be ineffective against acid attack.
Stainless steel has also been tried in various grades. While stainless steel is less prone to acidic attack, it does not possess the heat transfer characteristics or parameters of carbon steel. The results obtained therefore were an elevated off-gas temperature, and built up mechanical stresses that caused certain parts to fracture and break apart.
Breakdowns of one or more of the furnace components may occur in existing furnace systems due to one or more of the illustrative problems set forth above. When such a breakdown occurs, the furnace may need to be taken out of production for unscheduled maintenance to repair the damaged water cooled components. Since molten steel is not being produced by the steel mill during downtime, illustrative opportunity losses of as much as five thousand dollars per minute for the production of certain types of steel can occur. In addition to decreased production, unscheduled interruptions significantly increase operating and maintenance expenses.
In addition to the above described damage or harm to the water cooled components, fume ducts and off gas systems of both EAF and BOF systems are being damaged by corrosion and erosion. Damage to these areas of the furnace also results in loss of productivity and additional maintenance costs for mill operators. Furthermore, water leaks increase the humidity in the off-gasses, and reduce the efficiency of the bag house as the bags become wet and clogged. The accelerated erosion of these areas used to discharge furnace off-gasses illustratively is due to elevated temperatures and gas velocities caused by increased energy in the furnace. The higher gas velocities are due to greater efforts to evacuate all of the fumes for compliance with air emissions regulations. The corrosion of the fume ducts is due to acid formulation/attack on the inside of the duct caused by the meetings of various materials in the furnaces. The prior art teaches of the use of fume duct equipment and other components made of carbon steel or stainless steel. For the same illustrative reasons as stated above, these materials illustratively have proven to provide unsatisfactory and inefficient results. Commonly owned U.S. Pat. No. 6,890,479 to Manasek et al., the disclosure of which is now expressly incorporated herein by reference, as well as commonly owned U.S. patent application Ser. No. 10/828,044 of Manasek et al., the disclosure of which is now expressly incorporated herein by reference, each describe the use of improved heat exchange systems using alternative metal alloys, illustratively aluminum-bronze systems, having enhanced mechanical and physical properties over carbon or stainless steel cooling systems, for example, in that the alloy provides better thermal conductivity, hardness, and modulous of elasticity for the purposes of steel making in a furnace, thereby increasing the operational life of the furnace. However, such an alloy, or the use of other desirable metals, for example and without limitation copper, might cost more (in terms of the cost of the material itself and/or the cost of manufacture suitable for the particular material used) than would carbon or stainless steel.
Historically, then, a plurality of tubes of a uniform material and composition have been used to manufacture the heat exchange systems/water cooled elements described herein above. These tubes or pipes illustratively and generally were steel or some other alloy and had variable cross-sectional areas and internal diameters to meet the specific application requirement(s) or parameter(s) for heat transfer, wear characteristics, coolant velocities and other parameters. As noted, it may be desirable to use some metals or alloys, for example aluminum-bronze alloy, in lieu of others, for example steel in order to achieve desired operating characteristics or parameters. However, as also noted, the costs for tubes and pipes manufactured from such desired alloys, ceramics or other special materials, such as aluminum-bronze alloys for example, can be more expensive relative to using steel or cast iron for example.
A need exists for an improved heat exchange system and method for using same. Specifically, a need exists for an improved method and system wherein water cooled components and/or fume ducts remain operable as long as or longer than existing comparable components through the use of heat exchange systems having selectable operating characteristics or parameters, and selectable methods and materials of manufacture that allow for relatively high performance at relatively low cost.
The present disclosure may comprise one or more of the features identified in the various claims appended to this application and combinations of such features, as well as one or more of the following features and combinations thereof.
Provided is a pipe comprising:
an inner tube defined by a first inner boundary and a first outer boundary, the first inner boundary defining a hollow core having a core center; and
an outer tube overlaying the inner tube, the outer tube defined by a second inner boundary and a second outer boundary, the second inner boundary overlaying the first outer boundary;
wherein the composition or structure of the inner tube and the composition or structure of the outer tube differ in some respect relative to one another.
Also provided is a method of cooling an interior portion of a furnace comprising the steps of:                providing a pipe comprising:        an inner tube and an outer tube overlaying the inner tube;        equipping a piece of equipment with the pipe; and        directing a cooling fluid through the tubular section.        
The pipe may be coupled with a mounting member, such as for example and without limitation a plate. Another illustrative mounting member includes a bracket. The plate may be coupled together with the piece of equipment, which may be for example and without limitation a furnace.
The following materials have generally and illustratively been available for use in the pipes of heat exchange or protective systems: steel, cast iron, extruded steel, stainless steel, nickel alloys, copper, aluminum-bronze alloys, etc. The present disclosure will allow any desired combination of the above, or any other desirable metal, or other material including composites, to be used alone or in combination. For example, an inner tube may comprise a suitable, though relatively inexpensive material or metal such as for example and without limitation steel, suitable for transporting a liquid coolant. This inner tube may be overlaid or clad with a special/selected outer material, tube or pipe comprising a different, illustratively perhaps more expensive, material, such as for example and without limitation an aluminum-bronze alloy, with better operating characteristics or parameters relative to the inner tube material in the particular environment of operation. Illustratively, the outer layer or cladding may be produced by extruding a cladding tube/pipe onto the pipe/tube that forms the inside portion of the clad pipe. It will be appreciated that the outer material may be more expensive relative to the inner material or vice versa. So, too, the outer and inner material may be different grades or formulations of the same or similar material. In any event, it will also be appreciated that the outer material may have performance characteristics optimized for the environment in which it operates. It is also the case that the inner tube material may have better operating characteristics in the regime in which it operates (for example fluid transport), and may be more or less expensive than the outer material. In any event, the inner tube may have one or more characteristics or parameters that differ from those of the outer tube. Each of the inner and outer tube may have a differing construction or structure, for example and without limitation by varying the shape, cross-section, and/or materials of the respective inner and outer tubes, in order to emphasize one or more characteristics or parameters. The emphasis may seek, but need not seek to optimize the particular characteristic or parameter. Thus, the special clad tube/pipe illustratively will result in having the same or similar physical, abrasiveness resistance, chemical attack resistance, heat transfer, thermal attributes or other characteristics/parameters of a tube/pipe manufactured from 100% of the selected material except that the clad tube illustratively may have a lower overall cost, which itself may be a selected characteristic or parameter, and/or have better operating characteristics/parameters in one or more regimes. In the alternative, the outer and inner materials may be combined based on their different operating characteristics being optimized relative to one another for the regimes in which they operate. Therefore, illustratively in the case of a heat exchange or protective device incorporating pipes with an outer cladding of aluminum-bronze alloy, it will have a higher, relative to a steel pipe, thermal conductivity, resistance to etching by the stream of hot gasses (modulus of elasticity), and good resistance to oxidation, thereby increasing the life of the heat exchange system through reduced corrosion and erosion of the heat exchange system and related components. The combination of outer and inner materials may be necessary due to the need to have a pipe wall of a certain thickness, for example the heavy-walled pipes needed for use in portions of an EAF, without having to have the inner portions of that thickness comprised of a high-priced material. Similarly, as noted, the combination of materials could be selected to obtain optimum operating characteristics in different regimes. For example, the inner material could be selected to optimize the desired operating characteristics, for example fluid flow rate, in that regime, or to provide for the cost effectiveness, or some combination thereof; while the outer cladding is selected to better withstand the hot-side stresses relative to the material of the inner pipe or tube.
The disclosure illustratively will allow a wider flexibility and application of materials of construction that will improve equipment longevity plus on-line reliability and up-time because the equipment will be better suited to resist the effects of the high heat flux, corrosive and abrasive atmosphere in the furnaces, combustion chambers, flue gas systems, etc. equipment that are comprised of an assembly of such elements and at a potential cost savings.
It is anticipated that the present disclosure can be used in combination with other heat transfer equipment, such as condensers, shell and tube-type exchangers, finned exchangers, plate-and-frame-heat exchangers, and forced-draft air-cooled exchangers. In addition, it is anticipated that such other heat transfer equipment could itself benefit from using a combination of materials in accordance with the current disclosure. It is further anticipated that the current disclosure and any heat exchange system incorporating the present disclosure has other applications, such as cooling exhaust gasses from converting plants, paper manufacturing plants, coal and gas fired electrical power generation plants, and other exhaust gas generators, where the gasses are cooled for the purpose of capturing one or more components of the gas, where capture is effected by condensation, by carbon bed absorption, or by filtration.
Illustratively, the pipes can be cold rolled, hot rolled, drawn, extruded or cast. The pipes can be manufactured from ferrous metals, steel, copper, steel/ferrous alloy or copper alloys, nickel, titanium, bronze alloys including aluminum-bronze and nickel-bronze alloy alloys, and other suitable materials. The pipes can be seamless or welded in design as desired.
In summary, the disclosure illustratively will create a means to select a wider range of materials, operating characteristics and costs for manufacture of customer shaped and designed water cooled elements for steel, chemical. power and perhaps other industry applications. The elements will have the ability to better withstand the hostile and ever changing requirements in the furnaces, flue gas systems, off gas hoods, skirts, combustion chambers, drop out boxes etc. due to the inherent and improved coolant velocity within the element and the resulting increased heat transfer capability. This disclosure allows the selection of cladding materials that can be extruded onto an internal tube/pipe of different material at a required or desired cross-sectional radius to potentially optimize the operating characteristics in one or more regimes, for example heat transfer and elasticity requirements of the application, as desired and without limitation to current requirements to select the tube/pipe from generally uniform materials that are available on the commercial market.
These and other benefits and uses of the present disclosure will become more apparent from the following description of the illustrative embodiment.